Such changes in image size are required, in particular, for picture-in-picture (PiP) insertions, in the case of which a small image is faded into a main image. The image size of the small image is reduced for this purpose in proportion to the main image. For a known image reduction, reduction in a horizontal direction and in a vertical direction correspond to one another in this case, resulting in total reduction factors which correspond to reciprocal squares such as ¼, 1/9, 1/16, 1/36. The image signals thus reduced are read into an image memory together with the image signals of the main image for the purpose of synchronization, in which the pixels and lines occurring over the duration of a small image line or of the entire small image are stored, in order to achieve the change in image size.
A finer change in the horizontal reduction factor is possible, for example, by changing the read-out frequency of the image memory. A corresponding change in the vertical reduction factor is, however, not possible since the vertical frequency is fixed by the TV standard.